Since silicone resin compositions are less likely to undergo discoloration even upon high-temperature use, the silicone resin compositions have been generally used as photosemiconductor element encapsulation agents, optical adhesives, optical coating agents, and the like. However, in a case where a silicone resin is thermally cured in a binary liquid mixture type using a curing agent, there are in general some disadvantages that the silicone resin does not have sufficient handling ability or storage stability, after mixing a liquid silicone resin and a curing agent, that mixing is necessitated upon each use, and that its cost is also high. In view of the above, as an optical material that is usable in a single liquid type, an epoxy silicone that is relatively inexpensive and is capable of forming into a sheet by pre-curing is considered with expectation. For example, a thermosetting resin composition prepared by curing an epoxy silicone or the like with an aluminum compound catalyst has been disclosed (Japanese Patent Laid-Open No. 2007-332314).